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Differentiating
Diamond and its Imitations
By: Erum Qureshi
Summary: There are various
decisive tests to assess the
authenticity of a diamond. The Ceres
Diamond probe, Rayner Diamond
Tester, Diamond Pen are a few
popular instruments.
The distinctive appearance of a
well-cut diamond is based on the
effects of its adamantine luster,
the perfect flatness of its polished
facets, giving undistorted
reflections, and its fire, all these
due to its extreme hardness, high
refractive index and the skill with
which it is cut. Examination of the
girdle will often reveal naturals
(parts of the original crystal
deliberately left unpolished, to act
as a guide to the cutter and if
these show the typical trigons, they
are a clear indication that the
stone is a diamond. 'Nicks' in the
girdle can also be noticed.
The unique
hardness of diamond enables it
to scratch the polished surface of
synthetic corundum and no other
substance on earth can do this.
However, using hardness as a test is
considered crude and seldom
necessary since the diamond itself
may suffer some damage in doing so.
The most notable diamond Simulants
are synthetic cubic zirconia,
synthetic strontium titanate, YAG
(yttrium aluminium garnet) and GGG
(gadolinium gallium garnet).
Synthetic white spinel, made from
the Verneuil flame-fusion process is
also used as a substitute for small
diamonds in multiple gem settings;
moreover, it is singly refractive.
But it gives a
Refractometer reading of 1.726,
has a low degree of fire, and
measures 8 on
Moh's scale of hardness.
Synthetic rutile has six times the
dispersion of diamond but is easily
recognizable because of its high
refractive indices and a large
double refraction. YAG (yttrium
Aluminium garnet) has the appearance
of having properties of a diamond
Simulants, and is differentiated
from diamond by the Immersion
Contrast method.
Danger of confusion between diamond
and its simulants became much more
apparent when Cubic Zirconia
appeared on the market.
There was a demand for developing
special apparatus that would make
the distinction between diamond and
its Simulants rapid and certain,
even in the case of mounted stones
and with a very rudimentary
knowledge of gemology. The most
ingenious and effective method of
differentiating diamond from all
other gemstones makes use of its
outstanding property as a thermal
conductor, which is higher than for
any other substance - higher than
even copper or silver.
 The
Ceres Diamond probe was the first to
exploit this property even with
small specimens and in the case of
mounted stones. The Ceres probe has
two thermistors and a small copper
tip in a convenient holder. When the
instrument is switched on, the tip
of the probe warms up. When it is
gently held to the surface of the
stone to be tested, the needle of
the instrument swings to the right
and a green light flashes in case of
a diamond. With any other stone, the
needle of the meter swings to the
left and a red light flashes. The
probe of the Ceres instrument is
very delicate and needs handling
with care, but even very small
stones can be tested with it.
Another instrument of the same kind
is the British made Rayner Diamond
Tester. Such equipment is very
costly but to anyone dealing with
diamond jewelry, this is a
relatively small matter when
compared with the value of the goods
tested.
The
GIA has made use of another
property of diamond to differentiate
it from simulants. This particular
property is the diamond's affinity
for grease or greasy liquids. The
Gemological Institute of America has
produced a Diamond Pen, charged with
a specially prepared liquid, which
left a visible mark when drawn
across the table facet of a diamond,
but which broke up into droplets on
the surface of all other stones.
Another test for singling out a
diamond simulant is the Immersion
Contrast method. When light is
placed over stones (Strontium
titanate, YAG, GGG and CZ) immersed
in di-iodomethane (methylene iodide;
a high density liquid with a
refractive index of 1.742) or
Refractometer contact fluid (RI
1.81) different stones show
differing patterns. All except
strontium titanate show a dark ring
diminishing in width as their
refractive index approaches near to
that of the liquid. This is a
definite visual indication of
differentiation between diamond and
its simulant.
Another diamond simulant, though
very rare, is a diamond doublet. The
top half (crown) of this consists of
a diamond, which is cemented on to a
pavilion of some other colorless
stone. When such a stone is viewed
obliquely through the table facet, a
shadow of the edges of the facet can
be seen on the underlying cement
layer, revealing the fake.
Another way to differentiate between
a diamond and its simulant is ultra
violet radiation. Under long-wave
ultra-violet light, diamonds will
show a very varied degree of
fluorescence. If all the 'diamonds'
in a multi-stone setting show a
similar fluorescence, they are
certainly not diamonds. Under
X-rays, almost all diamonds show a
blue fluorescence and a brief
exposure on film will show diamonds
to be far more transparent to X-rays
than any other stone. This technique
is worth practicing as it is a
decisive test.
 image courtesy: http://nanoatlas.ifs.hr/index_2.html
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